Configuring overload state on a single SFM

When a router has fewer than the full set of SFMs functioning, the forwarding capacity can be reduced. Some scenarios include:

An overload condition can be set for IS-IS and OSPF to enable the router to still participate in exchanging routing information, but route all traffic away from it when insufficient SFMs are active. This is achieved using the following CLI commands:

- config>router>single-sfm-overload [holdoff-time hold-off-time]
- config>service>vprn>single-sfm-overload [holdoff-time hold-off-time]
- tools>perform>redundancy>forced-single-sfm-overload

These cause an overload state in the IGP to trigger the traffic reroute by setting the overload bit in IS-IS or setting the metric to maximum in OSPF. When PIM uses IS-IS or OSPF to find out the upstream router, a next-hop change in the IS-IS or OSPF causes PIM to join the new path and prune the old path, which effectively also reroutes the multicast traffic downstream as well as the unicast traffic.

When the problem is resolved, and the required compliment of SFMs become active in the router, the overload condition is cleared, which causes the traffic to be routed back to the router.

The conditions to set overload are:

Parent topic: Common configuration tasks